The European Commission, DG XI, has published an open invitation to tender for the preparation of a study synthesizing existing research on methods used for the calculation of the release of radioactivity following faults occurring in auxiliary buildings/annulus of pressurized water reactors (PWRs). The Commission, on the advice of its nuclear reactor safety working group (RSWG), commissioned a collaborative benchmark study to compare the methods used in Western Europe for calculating the release of radioactivity from faults taking place in the auxiliary building/annulus of a pressurized water reactor (PWR). In this context, study contracts were granted to Belgatom (Belgium), GRS (Germany), UNESA (Spain), (France) and NNC (United Kingdom). The objective of the present study is to synthesize the information provided in these five studies and to produce a report which will be presented to the RSWG and eventually published. The evaluation should include comparison and assessment of the licensing approaches in different countries and realistic methods of calculation as applied in each country. The study will focus on a break in the pipework of the chemical and volume control system (CVCS) in the auxiliary building/annulus of a PWR using the parameters agreed upon for the benchmark exercise. Each step in the calculation of the release will be considered in turn and conclusions drawn about where methods of calculation are currently similar and where they differ. The reasons for the observed discrepancies will be identified and those that are related to methodology will be separated from those that are due to design differences or operating procedures. The study should identify, if possible, an agreed realistic calculation route for evaluating the release of radioactivity from the faults specified above. The final report should also provide recommendations to the RSWG and serve as a reference document to designers and regulatory authorities in EU, central and east European countries providing a comprehensive and authoritative account of current realistic and conservative calculation methods. Tenderers must have a demonstrable background in the relevant aspects of nuclear power plant design with special emphasis on fluid systems design and thermo-hydraulics and radiological effects calculations. Requests for tender documentation should be sent to: European Commission DG XI Environment, Nuclear Safety and Civil Protection Mr V. Bhardwaj DG XI/A-2 200 rue de la Loi (BU5 3/158) B-1049 Brussels Tel. +32-2-2990889; Fax +32-2-2994449 Tenders should be sent to the same address.